SHANGHAI (Reuters) - The northeastern Chinese province of Jilin has cracked down on underground banks that funneled 45 billion yuan ($6.5 billion) worth of transactions, including one that serviced South Korean and Japanese workers, Xinhua reported.

A total of 18 cases have been investigated and 31 suspects arrested in the campaign by the Jilin police since the start of 2016, the Chinese state news agency said.

One case involved an underground bank that operated in Yanbian prefecture, near the North Korean border, which offered businessmen and workers from China, South Korea and Japan illegal cross-border exchange services, Xinhua said. The bank had made 11 billion yuan of transactions.

China has vowed to severely punish people involved in illegal fund transfers via underground banks and offshore companies, amid efforts to curb capital flight from the country to support the weakening yuan currency.

Jilin police are also working with banks and foreign exchange authorities to establish a system that will allow them to crack down on such activities in a timely fashion, the report said.